U.S. patent number 5,851,353 [Application Number 08/837,501] was granted by the patent office on 1998-12-22 for method for wet web molding and drying.
This patent grant is currently assigned to Kimberly-Clark Worldwide, Inc.. Invention is credited to Mark Wilson Fiscus, Thomas Garrett Neal, Jr..
United States Patent |
5,851,353 |
Fiscus , et al. |
December 22, 1998 |
Method for wet web molding and drying
Abstract
A method for can drying wet webs for tissue products to preserve
web bulk includes, in one embodiment, restraining a partially
dewatered wet web between a pair of sheet molding fabrics. The
restrained wet web is processed over a plurality of can dryers to
dry the wet web, for example from a consistency of at least about
40 percent to a consistency of at least about 70 percent. The sheet
molding fabrics in this embodiment protect the wet web from direct
contact with the can dryers and impart an impression in the web. A
can drying assembly and tissue machine for accomplishing the method
are also disclosed.
Inventors: |
Fiscus; Mark Wilson (Kaukauna,
WI), Neal, Jr.; Thomas Garrett (Appleton, WI) |
Assignee: |
Kimberly-Clark Worldwide, Inc.
(Neenah, WI)
|
Family
ID: |
25274634 |
Appl.
No.: |
08/837,501 |
Filed: |
April 14, 1997 |
Current U.S.
Class: |
162/113; 162/109;
162/117; 162/206 |
Current CPC
Class: |
B31F
1/126 (20130101) |
Current International
Class: |
B31F
1/00 (20060101); B31F 1/12 (20060101); B31F
001/12 () |
Field of
Search: |
;162/109,111,112,113,117,206,203,359.1,361 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0 604 824 A1 |
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Jul 1994 |
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EP |
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0 617 164 A1 |
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Sep 1994 |
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EP |
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0 677 612 A2 |
|
Oct 1995 |
|
EP |
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Primary Examiner: Chin; Peter
Attorney, Agent or Firm: Gage; Thomas M.
Claims
We claim:
1. A method of making a tissue sheet, comprising the steps of:
depositing an aqueous suspension of papermaking fibers onto an
endless forming fabric to form a wet web;
partially dewatering the wet web;
restraining the partially dewatered wet web between a pair of sheet
molding fabrics; and
processing the restrained wet web over a plurality of can dryers to
dry the wet web from a consistency of at least about 40 percent to
a consistency of at least about 70 percent.
2. A method of making a tissue sheet, comprising the steps of:
depositing an aqueous suspension of papermaking fibers onto an
endless forming fabric to form a wet web;
transferring the wet web to an air and liquid permeable perforated
belt arranged to form an endless loop;
transferring the wet web to the surface of a cylindrical drying
device;
creping the wet web from the cylindrical drying device when the wet
web has a consistency of at least about 40 percent;
restraining the creped wet web between a pair of sheet molding
fabrics; and
processing the restrained wet web over a plurality of can dryers to
dry the wet web to a consistency of at least about 70 percent.
3. The method of claim 1 or 2, wherein processing the restrained
wet web comprises passing the restrained wet web through an
impressioning section of a can drying assembly, the wet web
entering the impressioning section with a consistency of at least
about 45 percent.
4. The method of claim 3, wherein the wet web enters the
impressioning section with a consistency of from about 45 to about
65 percent.
5. The method of claim 3, wherein the wet web enters the
impressioning section with a consistency of from about 50 to about
60 percent.
6. The method of claim 1 or 2, wherein processing the restrained
wet web comprises passing the restrained wet web through an
impressioning section of a can drying assembly, the wet web exiting
the impressioning section and being released from between the sheet
molding fabrics with a consistency of at least about 75
percent.
7. The method of claim 6, wherein the wet web exits the
impressioning section and is released from between the sheet
molding fabrics with a consistency of from about 75 to about 85
percent.
8. The method of claim 1 or 2, wherein processing the restrained
wet web comprises passing the restrained wet web through a can
drying assembly having an impressioning section and a final drying
section, the wet web being restrained between the sheet molding
fabrics through the impressioning section and being released from
between the sheet molding fabrics prior to the final drying
section.
9. The tissue sheet made by the method of claim 1.
10. The tissue sheet made by the method of claim 2.
11. A method of making a tissue sheet, comprising the steps of:
depositing an aqueous suspension of papermaking fibers onto an
endless forming fabric to form a wet web;
transferring the wet web to an air and liquid permeable perforated
belt arranged to form an endless loop;
transferring the wet web to the surface of a cylindrical drying
device;
creping the wet web from the cylindrical drying device when the wet
web has a consistency of at least about 40 percent;
transferring the creped wet web to a sheet molding fabric;
processing the wet web while disposed on the sheet molding fabric
over a plurality of can dryers to dry the wet web to a consistency
of at least about 70 percent, the wet web and sheet molding fabric
alternately being directly in contact with the plurality of can
dryers; and transferring the wet web to a final drying section.
Description
BACKGROUND OF THE INVENTION
The present invention relates generally to methods and apparatuses
for making tissue products. More particularly, the invention
relates to methods and apparatuses for drying wet webs with can
dryers in a manner that maintains web bulk.
Bulk is an important property of tissue products such as facial and
bath tissue, napkins and paper towels. The bulk of a tissue
contributes to the actual and perceived softness and absorbency of
the tissue.
While a great deal of effort has been directed toward machine
configurations and processes for building bulk into a wet web, a
significant portion of that bulk is subsequently removed from the
wet web when it is dried to its final dryness. This appears to be
particularly the case with can dryers. In a conventional can drying
apparatus, the wet web is held between a dryer felt or dryer fabric
and the surface of each can dryer.
The effect of such a conventional can drying apparatus can be to
significantly decrease the bulk of the web. The repeated pressing,
releasing and pressing of the wet web against the can dryers can
function to iron the web. In a conventional afterdryer section
utilizing can dryers, for example, it is believed that the bulk of
a wet web can be decreased by as much as one-third or more from the
creping blade to the reel. As a consequence, the actual and
perceived softness and absorbency of the web is reduced.
Therefore, what is lacking and needed in the art is an improved can
drying process that does not iron a significant amount of bulk out
of the wet web when it is being dried. A related can drying
apparatus to achieve this result is also needed.
SUMMARY OF THE INVENTION
It has now been discovered that an improved web can be made in a
tissue machine by sandwiching the wet web between a pair of sheet
molding fabrics through at least a portion of the can dryer
assembly of the tissue machine. The wet web is protected from
directly contacting the can dryers by the sheet molding fabrics,
and because of the contact with the sheet molding fabrics, the wet
web is imparted with an impression of the sheet molding fabrics.
This is in contrast with prior efforts to design dryer fabrics that
supported the sheet against the dryer for optimum drying conditions
and did not mark the sheet.
Hence, in one embodiment, a method of making a tissue sheet
comprises the steps of depositing an aqueous suspension of
papermaking fibers onto an endless forming fabric to form a wet
web; partially dewatering the wet web; restraining the partially
dewatered wet web between a pair of sheet molding fabrics; and
processing the restrained wet web over a plurality of can dryers to
dry the wet web from a consistency of at least about 40 percent to
a consistency of at least about 70 percent.
The present method and apparatus are particularly beneficial when
utilized after the creping doctor and prior to the winding reel.
Thus, in one embodiment, a method of making a tissue sheet includes
the steps of depositing an aqueous suspension of papermaking fibers
onto an endless forming fabric to form a wet web; transferring the
wet web to an air and liquid permeable perforated belt arranged to
form an endless loop; positioning the wet web on the surface of a
cylindrical drying device; removing the wet web from the
cylindrical drying device using a creping blade while the wet web
has a consistency of at least about 40 percent; restraining the
creped wet web between a pair of sheet molding fabrics; and
processing the restrained wet web over a plurality of can dryers to
dry the wet web to a consistency of at least about 70 percent.
Contact between the wet web and the sheet molding fabrics adds bulk
to the wet web and impresses the desired repeating pattern on both
sides of the wet web. The visual markings may be perceived by
consumers as more cloth-like or pleasing, and therefore give the
tissue an added benefit.
Additionally, by sandwiching the wet web between two sheet molding
fabrics, the wet web does not directly contact the can dryer
surfaces. The existing bulk in the wet web, imparted by creping or
other techniques, is not ironed out of the web by repeatedly being
pressed in direct contact with the drying cans. In some instances,
however, it may be desirable to maintain and/or build less bulk
into the web in favor of improved drying efficiency. Thus, in one
alternative embodiment, a method of making a tissue sheet includes
the steps of depositing an aqueous suspension of papermaking fibers
onto an endless forming fabric to form a wet web; transferring the
wet web to an air and liquid permeable perforated belt arranged to
form an endless loop; positioning the wet web on the surface of a
cylindrical drying device; removing the wet web from the
cylindrical drying device using a creping blade while the wet web
has a consistency of at least about 40 percent; transferring the
creped wet web to a sheet molding fabric; and processing the wet
web while disposed on the sheet molding fabric through a plurality
of can to dryers to dry the wet web to a consistency of at least
about 70 percent.
The present method may also improve the cross direction stretch of
the resulting tissue. The tissue would then be more durable and
flexible than would otherwise be possible at the same tensile
level, which means that the tissue can be embossed harder before
fracturing. Further, by molding the wet web and reducing compacting
of the wet web during can drying, the absorbent capacity of the web
should also increase.
The fiber consistency of the wet web should be sufficiently low
while in contact with the sheet molding fabric or fabrics to permit
impressioning by the fabric. In particular embodiments, the wet web
enters the impressioning section of the can drying assembly with a
consistency of at least about 40 percent, such as from about 40 to
about 80 percent. More particularly, the wet web enters the
impressioning section of the can drying assembly with a consistency
of at least about 45 percent, for instance from about 45 to about
65 percent, and more particularly from about 50 to about 60
percent, for improved performance. These consistencies are
particularly suited for bath tissue, facial tissue, napkins and
toweling may be different for other paper grades. The terms
"consistency" and "fiber consistency" are used interchangeably
herein to refer to the weight percent fiber in an aqueous fiber
suspension, a stock layer, or a dewatered or dried web.
Once a sufficiently high fiber consistency is obtained, the wet web
may be released from contact with the sheet molding fabric or from
position between the sheet molding fabrics for further drying. In a
particular embodiment, for example, the can drying assembly
includes a final drying section downstream of the impressioning
section. It is believed to be advantageous, for instance, to
release the wet web from contact with the sheet molding fabric or
from position between the sheet molding fabrics upon exiting the
impressioning section when the wet web reaches a consistency of at
least about 70 percent, and more particularly at least about 75
percent, such as from about 75 to about 85 percent, and even more
particularly from about 80 to about 85 percent, for improved
pattern definition, bulk and efficiency. Drying the wet web after
being released from between the sheet molding fabrics at the stated
consistencies is not believed to significantly detract from the web
bulk.
In another aspect of the invention, a can drying assembly for
processing a wet web comprises a plurality of can dryers including
a first can dryer and a last can dryer. A pair of sheet molding
fabrics are each arranged to form an endless loop, and fabric
handling means cause a portion of each endless loop to be united in
a common run from the first can dryer to the last can dryer.
In one particular embodiment, a machine for manufacturing tissue
products comprises a forming fabric adapted to form an endless loop
and a means for depositing an aqueous suspension of papermaking
fibers onto the forming fabric to form a wet web. An air and liquid
permeable perforated belt of the machine is arranged to form an
endless loop. The machine also includes means for transferring the
wet web from the forming fabric to the perforated belt, a
cylindrical drying device, and means for directing the wet web from
the perforated belt into operable relation with the cylindrical
drying device. A can drying assembly of the machine comprises an
impressioning section having a plurality of can dryers and a pair
of sheet molding fabrics that each form an endless loop. The sheet
molding fabrics are disposed adjacent one another and form a common
run over a portion of each endless loop. The common run is
operatively associated with the plurality of can dryers. The
machine also includes means for transferring the wet web from the
cylindrical drying device to the impressioning section, such that
the wet web is sandwiched between the sheet molding fabrics.
As used herein, the term "cylindrical drying device" refers to
rotating drums for drying wet webs and includes throughdryers,
Yankee dryers, and can dryers. The terms "throughdryer" and
"throughdrying" are used herein to refer to rotating drums having
heated air passing through the drum surface and through the wet web
to remove moisture and dry the web. The term "Yankee dryer" is used
herein to refer to a rotating, solid surface, drum wherein the wet
web is adhered to the surface and removed therefrom by creping or
the like. Yankee dryers are usually heated to remove moisture and
dry the web, although they can be unheated and used exclusively for
creping. The terms "can dryers," "can drying" and "drying cans" are
used herein to refer to rotating, solid surface heated drums
wherein the wet web is not adhered to the drum surface such that is
must be removed by creping or comparable techniques.
The sheet molding fabrics used in the impressioning section of the
can drying assembly are constructed to maintain web bulk and/or
impart bulk to the web. Thus, the sheet molding fabrics suitably
include, without limitation, those papermaking fabrics that exhibit
significant open area or three dimensional surface contour or
depressions sufficient to impart a significant degree of
z-directional impressioning of the web. Such fabrics include
single-layer, multi-layer, or composite permeable structures.
Preferred fabrics have at least some of the following
characteristics: (1) On the side of the sheet molding fabric that
is in contact with the wet web (the outer side), the number of
machine direction (MD) strands per inch (mesh) is from 10 to 200
and the number of cross-machine direction (CD) strands per inch
(count) is also from 10 to 200. The strand diameter is typically
smaller than 0.050 inch; (2) On the outer side, the distance
between the highest point of the MD knuckle and the highest point
of the CD knuckle is from about 0.001 to about 0.02 or 0.03 inch.
In between these two levels, there can be knuckles formed either by
MD or CD strands that give the topography a three-dimensional
characteristic and which may be impressioned in the web during can
drying; (3) On the outer side, the length of the MD knuckles is
equal to or longer than the length of the CD knuckles; (4) If the
fabric is made in a multi-layer construction, it is preferred that
the bottom layer is of a finer mesh than the top layer so as to
control the depth of web penetration; and (5) The fabric may be
made to show certain geometric patterns that are pleasing to the
eye, which typically repeat between every 2 to 50 warp yarns.
Specific suitable sheet molding fabrics include, by way of example,
those made by Appleton Mills, Appleton, Wis. and designated as
numbers P57, P116 and T 124-10. Particular sheet molding fabrics
that may be used also include the fabrics disclosed in U.S. Pat.
No. 5,429,686 issued Jul. 4, 1995, to Chiu et al., which is
incorporated herein by reference.
The forming process and tackle can be conventional as is well known
in the papermaking industry. Such formation processes include
Fourdrinier, roof formers (such as suction breast roll), gap
formers (such as twin wire formers, crescent formers), or the like.
Forming wires or fabrics can also be conventional, with the finer
weaves with greater fiber support being preferred. Headboxes used
to deposit the fibers onto the forming fabric can be adapted to
form layered or nonlayered webs.
The method disclosed herein can be applied to any tissue web, which
includes webs for making facial tissue, bath tissue, paper towels,
napkins, or the like. Such tissue webs can be single-ply products
or multi-ply products, such as two-ply, three-ply, four-ply or
greater. One-ply products are advantageous because of their lower
cost of manufacture, while multiply products are preferred by many
consumers. For multi-ply products it is not necessary that all
plies of the product be the same, provided at least one ply is in
accordance with this invention. The webs can be layered or
unlayered (blended), and the fibers making up the web can be any
fibers suitable for papermaking.
Suitable basis weights for these tissue webs can be from about 5 to
about 70 grams per square meter (gsm), preferably from about 10 to
about 50 gsm, and more preferably from about 30 to about 50 gsm.
For a single-ply towel, a basis weight of about 40 gsm is
preferred. For a single-ply bath tissue, a basis weight of about 25
gsm is preferred. For a two-ply tissue, a basis weight of about 20
gsm per ply is preferred. For a three-ply tissue, a basis weight of
about 15 gsm per ply is preferred.
Numerous features and advantages of the present invention will
appear from the following description. In the description,
reference is made to the accompanying drawings which illustrate
preferred embodiments of the invention. Such embodiments do not
represent the full scope of the invention. Reference should
therefore be made to the claims herein for interpreting the full
scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic flow diagram of a tissue making apparatus
used to practice a method of the present invention.
FIG. 2 representatively shows an isolated view of an after dryer
section of the tissue making apparatus of FIG. 1.
FIG. 3 representatively shows a view similar to FIG. 2 but
illustrating an alternative after dryer section.
FIG. 4 representatively shows an isolated view of another
alternative after dryer section.
DETAILED DESCRIPTION OF THE INVENTION
The invention will now be described in greater detail with
reference to the Figures. Unless otherwise indicated, conventional
papermaking apparatus and operations can be used with respect to
the headbox, forming fabrics, web transfers, drying and creping,
all of which will be readily understood by those skilled in the
papermaking art. Nevertheless, various conventional components are
illustrated for purposes of providing the context in which the
various embodiments of the invention can be used.
One embodiment of a method and apparatus for manufacturing a tissue
is representatively shown in FIG. 1. For simplicity, the various
tensioning rolls schematically used to define the several fabric
runs are shown but not numbered. A papermaking headbox 20 injects
or deposits an aqueous suspension of papermaking fibers 21 onto an
endless forming fabric 22 traveling about a vacuum breast roll 23.
The forming fabric 22 allows partial dewatering of a newly-formed
wet web 24 to a consistency of about 10 percent.
While supported on the forming fabric 22, the wet web 24 may be
dewatered further by one or more optional vacuum or suction boxes
26. The consistency of the wet web 24 immediately downstream of the
optional dewatering boxes 26 may be from about 10 to about 30
percent. The Fourdrinier former illustrated is particularly useful
for making heavier basis weight sheets useful as wipers and towels,
although other forming devices such as twin wire formers, crescent
formers or the like can be used instead. Hydroneedling, for example
as disclosed in U.S. Pat. No. 5,137,600 issued Aug. 11, 1992 to
Barnes et al., can optionally be employed to increase the bulk of
the web.
The wet web 24 is then transferred from the forming fabric 22 to an
air and liquid permeable perforated belt 30 that is arranged to
form an endless loop. A pickup device 32, for example a vacuum
pickup roll, a transfer shoe or the like, is generally employed to
transfer the wet web 24 to the perforated belt 30. Alternatively,
the negative pressure pickup device 32 can be supplemented or
replaced by the use of a positive pressure device (not shown) on
the opposite side of the wet web 24 to blow the web onto the
perforated belt 30. The perforated belt 30 may be traveling at the
same speed as the forming fabric 22, or a slower speed if
desired.
The perforated belt 30 may comprise a conventional papermaking felt
or a transfer fabric. Suitable fabrics or felts are available from
Appleton Mills and are identified as AMFLEX 25.
In the illustrated embodiment, a press roll 34 is disposed within
the endless loop of the perforated belt 30 and functions to press
the wet web 24 onto the surface of a Yankee dryer 36. A drying hood
37 may be used in conjunction with the Yankee dryer 36.
Mechanically pressing the wet web between the perforated belt 30
and the dryer surface squeezes some of the water from the wet web
and adheres the web to the dryer surface. The wet web 24 is removed
from the dryer surface with a creping blade 38. Creping adhesives,
release agents or the like, which are well known in the art, may be
applied to the surface of the Yankee dryer 36 following the creping
doctor to improve dryer operation.
In one embodiment, the consistency of the wet web 24 as it
approaches the press roll 34 is from about 8 to about 35 percent.
Following the press roll 34, the consistency of the web is from
about 30 to about 50 percent. The Yankee dryer steam pressure and
hood drying capability are desirably controlled so that the
consistency of the wet web 24 immediately after being removed from
the Yankee dryer is at least about 40 percent, and particularly
from about 50 to about 60 percent.
The wet web 24 is subsequently transferred to a can drying assembly
40 specifically configured to maintain or increase the bulk of the
web and to remove moisture and dry the web. The can drying assembly
40 is shown in greater detail in FIG. 2, where components similar
to those previously described have been given the same reference
numeral. The illustrated can drying assembly 40 comprises an
impressioning section 42 having a plurality of can dryers 44 and a
pair of sheet molding fabrics 46 and 48. The exact number of can
dryers 44 may vary depending on the desired increase in dryness of
the wet web 24, machine speed, basis weight, and similar factors.
In one particular embodiment, the impressioning section 42 could
include 15 can dryers operating at 100 pounds per square inch
(psi).
Each of the sheet molding fabrics 46 and 48 forms an endless loop.
The various fabric handling rolls are configured so that the sheet
molding fabrics 46 and 48 are disposed adjacent one another over a
portion of their endless loops, thus defining a common fabric run
49 that is operatively associated with the can dryers 44. As
illustrated, the common fabric run 49 follows a serpentine path
over all of the can dryers 44 of the impressioning section 42. The
can drying assembly 40 may include other drying devices or fabric
runs (see FIG. 3) in addition to those of the impressioning section
42.
The wet web 24 is transported across an open draw from the creping
doctor 38 to the impressioning section 42 and is then sandwiched
between the sheet molding fabrics 46 and 48. The wet web 24 remains
restrained between the fabrics 46 and 48 from the first can dryer
44 through the last can dryer 44 of the impressioning section.
Thus, one of the sheet molding fabrics 46 or 48 is disposed between
the wet web 24 and each of the can dryers 44. In the embodiment of
FIGS. 1 and 2, the wet web 24 is final dried to a consistency of
about 94 percent or greater in the impressioning section 42 and is
thereafter transported to a reel 50 and a reel spool 51 where the
wet is wound into a roll 52 for subsequent conversion into the
final product form. Prior to being wound onto the reel spool 51,
the dried wet web 24 can be carried through one or more optional
fixed gap embossing or calendering nips 54.
To retain and/or build the bulk of the wet web 24, the web
desirably enters the impressioning section 42 of the can drying
assembly 40 with a consistency of at least about 40 percent, such
as from about 40 to about 80 percent. More particularly, the wet
web enters the impressioning section 42 with a consistency of at
least about 45 percent, for instance from about 45 to about 65
percent, and more particularly from about 50 to about 60 percent,
for improved performance.
The wet web 24 may exit the impressioning section 42 sufficiently
dry, for example greater than about 94 percent consistency, for
winding onto the reel spool 51. Alternatively, the wet web 24 may
exit the impressioning section 42 and be released from between the
sheet molding fabrics 46 and 48 with a consistency of at least
about 70 percent, at which point further noncompressive drying
methods may be employed without significantly decreasing the
existing bulk of the web. In particular embodiments, though, the
wet web 24 desirably exits the impressioning section 42 with a
consistency of at least about 75 percent, such as from about 75 to
about 85 percent, and more specifically from about 80 to about 85
percent, for improved pattern definition, bulk and performance. At
lower consistencies the desired repeating pattern will still be
impressed upon the web, but web bulk may not be maintained through
the final drying section. Under such circumstances, the wet web 24
may undergo additional drying beyond the impressioning section 42
prior to winding. Other suitable noncompressive drying methods
which tends to preserve the bulk or thickness of the wet web
include, without limitation, throughdrying, infra-red irradiation,
microwave drying, or the like.
An alternative can drying assembly 60 for use with the tissue
manufacturing process of FIG. 1 is illustrated in FIG. 3. Again,
components similar to those previously described have been given
the same reference numeral for purposes of consistency and
simplicity. The can drying assembly 60 comprises an impressioning
section 42 and a final drying section 62. The impressioning section
42 is similar to that described in relation to FIGS. 1 and 2 except
that the number of can dryers 44 has been reduced. In one
particular embodiment, the impressioning section 42 includes 5 can
dryers 44 operating at 100 psi.
The wet web 24 is restrained between the pair of sheet molding
fabrics 46 and 48 through the impressioning section 42, but is
desirably released from between the sheet molding fabrics prior to
the final drying section 62. The consistency of the wet web 24 when
exiting the impressioning section 42 is desirably at least about 70
percent, and more particularly at least about 75 percent, such as
from about 75 to about 85 percent or from about 80 to about 85
percent, for improved performance.
The final drying section 62 functions to remove moisture and dry
the web to its final dryness. The final drying section 62 comprises
a plurality of can dryers 64 and a pair of dryer fabrics or felts
66 and 68. The exact number of can dryers 64 in the final drying
section 62 may vary depending on the incoming dryness, the desired
final dryness, the size and operating parameters of the can dryers,
and similar factors. By way of illustration, the final drying
section 62 may include 10 can dryers 64 operating at 80 psi.
Each of the dryer fabrics or felts 66 and 68 forms an endless loop
and is arranged to transport the wet web 24 through a serpentine
path over the can dryers 64 of the final drying section 62. As
illustrated in FIG. 3, the lower dryer fabric 68 guides the wet web
24 over the first can dryer 64 of the final drying section 62 and
every second can dryer 64 thereafter. Correspondingly, the upper
dryer fabric 66 guides the wet web 24 over the second can dryer 64
of the final drying section 62 and every second can dryer 64
thereafter. The fabrics 66 and 68 of the final drying section 62
need not form a common fabric run to sandwich the web therebetween,
as was the case in the impressioning section 42. The can drying
assembly 60 may include alternative or additional drying devices or
fabric runs besides the final drying section 62 (not shown).
A further alternative can drying assembly 70 for use with the
tissue manufacturing process of FIG. 1 is illustrated in FIG. 4.
The can drying assembly 70 may be particularly useful in instances
when it is desirable to maintain and/or build less bulk into the
web in favor of improved drying efficiency. The can drying assembly
70 comprises an impressioning section 72 and a final drying section
62. The impressioning section 72 comprises a plurality of can
dryers 64 and a single sheet molding fabric 46. The final drying
section 62 may be identical to the final drying section 62
described in relation to FIG. 3.
In this embodiment, the wet web 24 is transferred from the creping
blade 38 to the sheet molding fabric 46 while the wet web has a
consistency of at least about 40 percent. At this point, the wet
web 24 is processed through all of the can dryers 44 of the
impressioning section 72 while disposed on the single sheet molding
fabric 46. Fabric 48 is used to assist in web control, particularly
when threading the web through the impressioning section. Fabric 48
can be a conventional dryer fabric, or optionally an impressioning
fabric. The wet web 24 and the sheet molding fabric 46 alternate
being disposed directly in contact with the can dryers 44 in the
impressioning section 72. The wet web 24 is thereafter removed from
the sheet molding fabric 46 and transferred to the final drying
section 62.
The foregoing detailed description has been for the purpose of
illustration. Thus, a number of modifications and changes may be
made without departing from the spirit and scope of the present
invention. For instance, alternative or optional features described
as part of one embodiment can be used to yield another embodiment.
Additionally, two named components could represent portions of the
same structure. Therefore, the invention should not be limited by
the specific embodiments described, but only by the claims.
* * * * *